The present invention relates to a method of and apparatus for controlling a pulse controlled, constant speed brushless motor actuated by a predetermined frequency with less speed-irregularity or cogging, the motor being used particularly for, though not limited to, direct-driving a capstan for a tape recorder, drum drive mechanism for facsimiles, and disc rotation mechanism for floppy disc drives. More particularly, the present invention relates to a method of and apparatus for accelerating immediately and automatically a rotation of the motor up to a predetermined rotational speed when the motor is started to rotate, or otherwise when the motor is decelerated by some reasons. In the present application, the term "pulse controlled brushless motor" intends to mean a motor which has a structure similar to that of so-called a stepping motor and rotates continuously with a minimum speed irregularity in synchronization with continuous pulse signal inputs.
The pulse controlled brushless motor of the type described will not start to rotate even when the motor is supplied with a pulse train of a predetermined operational pulse rate which is higher than the maximum pull-in pulse rate correspondent to a load of the motor. An attempt has been made in which pulse trains are provided, at the beginning, with a pulse rate lower than the maximum pull-in pulse rate and progressively increasing the pulse rate to a final, desired pulse rate, when an input pulse rate correspondent to a motor speed is higher than the maximum pull-in pulse rate. Accordingly, the input pulse rate should be swept into the slewing pulse rate range by utilizing a variable frequency oscillator every time when the motor is to be started to rotate or when the motor is overloaded by some reasons.